replacing check valve on submersable pump???

My pump is about 280 feet deep and is cycling about every 7 minutes. I think it has been doing this for some time but I just moved it to a well house from a tight crawl space under house so I can diagnose better. I installed a new pressure tank and switch hoping it would help, it did need the tank as there was water on both sides of bladder. If I close the valve I installed before the tank it holds pressure. Does this sound like it is a check valve on the pump? Jay

Thanks DonL. Thats what I was afraid of, dont really know how to pull up nearly 300 feet of pipe and pump but I have to figure it out. Hey is the check valve attached to the pump or internal to the pump? Thanks Jay

A 300' well pump is best done by a professional! It can be done by a DIY but one mistake could cost you thousands. A temporary check valve near the tank is a bandaid for the real problem. You can add a check valve just above the pump but if you do I'd recommend removing the guts from the pump check valve.